This invention relates to the formation and control of a high temperature, high energy plasma and more particularly to an electrode structure which allows the formation and focusing of such plasmas for production and control of energy.
The use of high energy, high temprature plasmas has become more prevalent with development of technologies such as magnetohydrodynamics and nuclear fusion; it has become advantageous to generate such plasmas, to produce energy and neutrons from them and to control reaction products derived therefrom, by means of plasma focus technology.
One means that has been contemplated for control of plasmas is "Z pinch" type thermonuclear reactor. In one such reactor, a neutron moderating blanket, formed of a liquid lithium vortex, is caused to swirl concentric about a hollow electrode. To form the pinch, solid or liquid may be injected through the electrode to cause an arc to occur between the electrode and bottom of the vortex of lithium. Deuterium/Tritium fuel may then be injected along the electrode axis, forming a Z pinch in the vortex between the inserted electrode and the lithium blanket which serves as a return conductor. The plasma Deuterium/Tritium fuel in the pinch is electrically energized by an arc sufficient to cause liberation of neutrons from the fuel plasma located in the pinch.
Plasma focus reactors on the other hand, utilize a moving electric discharge to compress the fuel plasma and to concentrate the plasma at a particular location, i.e., a focus, where the compression also achieves adiabatic compression of the fuel plasma. Such adiabatic compression with anomalous ion heating, achieved in pulselike successions, causes the liberation of neutrons from the plasma in the focus.
The utilization of Z-pinch or plasma focus reactors which employ a lithium vortex yield several advantages. It has been suggested that, because such structures can confine fuels at high temperature without continuous strong magnetic fields used in other reactor designs, high costs associated with the production of such fields are reduced by the provision of the lithium blanket that effects containment. The lithium blanket also breeds tritium when absorbing the neutrons liberated in either the "pinch" or the focus; tritium so produced is a useful byproduct, forming a portion of the Deuterium/Tritium fuel used by itself. The lithium blanket is also efficient at converting the kinetic energy of the liberated neutrons into recoverable heat and is stable against structural failure and corrosion at operating temperatures under neutron irradiation.
Plasma focus reactors also promise enhanced liberation of neutrons as well, and have been able to liberate many orders of magnitude more neutrons from the plasma fuel than either magnetic containment reactors, Z-pinch reactors, or laser fusion reactors. Although ion heating mechanisms and subsequent neutron production in a dense plasma focus is not yet well understood, formation of a plasma focus can be predicted using existing two dimensional magnetohydrodynamic (MHD) simulation. Imshennik et al.sup.1 have been able to derive a proportionality formula for neutron yield in plasma focus reactors that assumes constant source inductance for a plasma focus. Such a formulation is shown in equation 1. EQU W.about.C-.sup.-1/14 .times. E.sup.22/7 (Eq. 1) FNT .sup.(1) V. S. Imshennik, N. W. Fillipov, T. I. Filippova, Nucl. Fusion 13 (1973)
In this equation W is the neutron yield, C is the capacitance of a capacitive discharge bank powering the focus and E is the stored energy. For a focus producing a 10 megajoule liberation of thermal neutrons, with a capacitance C of about 500 .mu.F at 200 kilovolts, the equation would predict in the range of 4 .times. 10.sup.16 neutrons per pulse using deuterium in the focus. It is believed that the yield may be increased by a factor of 100 if a larger cross-section Deuterium/Tritium reaction is exploited in the focus. A yield of 4 .times. 10.sup.18 reactions of a 17.58 eV energy reaction corresponds to greater than 10 megajoules product per pulse, particularly considering possible energy multiplication in a lithium blanket from the product of tritium via the Li.sup.6 (n, .alpha.)H.sup.3 reaction or any of the other energy multiplication schemes, for example, such as have been described by Lidsky.sup.2. FNT .sup.(2) L. N. Lidsky, Nucl. Fusion 15 (1975) 151.
A plasma focus reactor has several practical advantages over other proposed fusion reactor schemes. Aside from being the most prolific source of fusion neutrons extant and exhibiting encouraging scaling with increasing energy input, it represents a significant decrease in the basic plant capital cost. In contrast to magnetic containment such as a tokamak reactor schemes, it requires no large and expensive cryogenic magnet assemblies which are as yet undeveloped. It, also, requires no high power, high repetition rate lasers as in the laser fusion schemes. Geometry considerations favor the focus in terms of both shielding and maintenance. The liquid lithium outer electrode and neutron blanket suffers no structural radiation damage and the central electrode structure can be adequately shielded and easily replaced when necessary. This is in contrast to the tokamak reactors, which would require periodic replacement of the inside liner of a toroidal vacuum vessel, as well as the laser reactors, which require the replacement of the inner surface of a spherical vacuum chamber. The high power density of the focus lends itself to a very compact nuclear island with resulting small size yielding savings both in materials and biological shields. Finally, the high voltage, high energy capacitor bank which would power a focus reactor is an easily achievable application of presently existing technology.
A further drawback encountered in plasma containment schemes which utilize magnetic fields generated by cryogenic magnets for plasma containment is the formation of radioactivity in solid containment walls and resulting structural weakness therein caused by the bombardment thereof by thermal and fast neutrons. Of course, as the density of liberated neutrons increases, these effects become more severe, and pose serious drawbacks to the creation of any large-scale exotermic fusion reactors. Z-pinch and plasma focus reactors also are susceptible to radiation damage of their anode structures, the Z-pinch reactors having a larger problem in this regard as neutrons are propagated from a larger volume than from the relatively smaller volume of the focus where neutrons ar liberated in focus reactors.